1. Field of the Invention
This application relates to compensation circuits utilized on integrated circuits.
2. Description of the Related Art
Compensation circuits compensate for process, temperature, and other variable conditions that affect circuit performance. Compensation circuits typically work by measuring the circuit's performance against a known reference parameter such as voltage or current. A typical compensation circuit 10 is shown in FIG. 1 in which a known reference voltage is supplied on node 11. An input/output terminal 13 is coupled to a power supply node (VDD) through external resistor 15. Comparator 17 compares the voltage present on I/O terminal 13 with the reference voltage supplied on node 11. The compensation circuit adjusts the voltage on I/O terminal 13 by selectively enabling field effect transistors (FETs) 12, 14, and 16 to be substantially equal to the reference voltage supplied on node 11. Note that although three FETs 12, 14, and 16 are shown, the number of FETs utilized in a typical compensation circuit is much higher.
Often multiple compensation circuits are required to account for differences in circuit design types and locations. However, in current compensation schemes, the I/O terminal and external resistor 15 are dedicated to a single compensation circuit precluding the I/O terminal and the resistor from being shared among multiple compensation circuits. As die size and complexity increase, the number of compensation circuits also tends to increase. An increasing number of external resistors requiring separate I/O terminals places a burden on the package, especially if the pins in a particular design are fixed due to compatibility requirements with earlier designs. It would be desirable to find an improved compensation approach that reduces the pin and resistor cost associated with the increasing need for compensation circuits.